Synthesis of oxaspiro[m.n] skeletons based on the Nicholas reaction

Treatment of alkyne–Co2(CO)6 complexes possessing a methylidene moiety as well as a terminal hydroxy functionality with SnCl4 at 0°C effected tandem ring-closure reactions resulting in the formation of 1-oxaspiro[4.4]nonane, 1-oxaspiro[4.5]decane, 6-oxaspiro[4.5]decane, and 1-oxaspiro[5.5]undecane frameworks in high yields.